The present invention relates to a package structure of a semiconductor device. More particularly, it relates to a package structure of a semiconductor device having a BGA (ball grid array) structure in which balls used in soldering when mounting a semiconductor device on a product are arranged at the back side of a substrate in a matrix.
A conventional semiconductor device comprises a BGA substrate, a semiconductor chip disposed on the BGA substrate, a heat spreader for dispersing the heat generated on the semiconductor chip externally, and a ring for keeping a specific interval between the BGA substrate and heat spreader and joining the two. The BGA substrate has a multilayer structure in which plural insulating substrates are laminated, and plural wires and via holes are formed in each insulating substrate. The BGA substrate is formed by mutually connecting specified wires through via holes when laminating plural substrates, and the plural wires cross three-dimensionally through the insulating substrates, so that the semiconductor device can be reduced in size.
FIG. 4 is a partially cut-away perspective explanatory diagram showing an example of a conventional semiconductor device. In FIG. 4, reference numeral 1 denotes a plastic substrate which is a BGA substrate, 2 denotes a semiconductor chip, 3 denotes a heat spreader, 4 denotes a ring, 6 denotes a solder ball, and 8 denotes a sealing member.
Each line (not shown) provided on the plastic substrate 1 is connected electrically to an external electrode (not shown) of the semiconductor device. Solder balls 6 are made of solder, and are electrically connected to the external electrode of the semiconductor device. Plural electrodes (not shown) of the semiconductor chip 2 are electrically connected to the specified lines of the plastic substrate 1, respectively. Such connection is realized, for example, by forming preliminarily solder bumps on each electrode surface of the semiconductor chip 2 and external electrode surface connected to each line of the plastic substrate 1, and soldering by using these solder bumps. The sealing member 8 is composed of a synthetic resin for sealing, and is provided in order to connect the semiconductor chip 2 tightly to the plastic substrate 1. That is, the sealing member 8 is provided in order to prevent breakage at the connection of the lines of the plastic substrate 1 and electrodes of the semiconductor chip 2 due to warp of plastic substrate or the like.
The ring 4 has an opening in the center of a plate member, and the shape of the opening is determined depending on the shape of the semiconductor chip 2. The shape of the heat spreader 3 is a thin plate similar to the shape of the plastic substrate 1, and the semiconductor chip 2 and heat spreader 3, plastic substrate 1 and ring 4, and heat spreader 3 and ring 4 are adhered together by adhesives. The adhesives for adhering the semiconductor chip 2 and heat spreader are adhesives having a high heat releasing property, for example, silicone or epoxy derivative. On the other hand, the adhesive for adhering the plastic substrate 1 and ring, and heat spreader 3 and ring 4 is a film adhesives of, for example, epoxy resin.
An example of manufacturing method of the semiconductor device is described below. FIGS. 5(a) to 5(d) and FIGS. 6(a) to 6(c) are process sectional explanatory views showing an example of a manufacturing method of a conventional semiconductor device. In FIGS. 5(a) to 5(d) and FIGS. 6(a) to 6(c), same parts as in FIG. 4 are identified with same reference numerals. Reference numeral 5a denotes a first solder bump electrically connected to an electrode (not shown) contained in the semiconductor chip 2, and 5b denotes a second solder bump electrically connected to an end (not shown) of plural lines provided in the plastic substrate 1. Reference numeral 7a denotes a first adhesive layer comprising an adhesive for adhering the plastic substrate 1 and ring 4, and heat spreader 3 and ring 4, and 7b denotes a second adhesives layer comprising adhesives for adhering the semiconductor chip 2 and heat spreader 3.
At the beginning, the first solder bump 5a is provided on the electrode contained in the semiconductor chip 2, and similarly the second solder bump 5b is provided on one end of plural lines of the plastic substrate 1 (see FIG. 5(a)). Next, on the surface of the plastic substrate 1, a flux material is applied in the region in which the second solder bump 5b is formed. The semiconductor chip 2 is mounted on the plastic substrate 1, and the first solder bump 5a and second solder bump 5b are brought into mutual contact, and the plastic substrate 1 and semiconductor chip 2 are charged into a heating furnace (so-called reflow furnace). As a result, the first solder bump 5a and second solder bump 5b are melted, and the mutually contacting first solder bump 5a and second solder bump 5b are formed into one body. In FIGS. 5(a)-5(d), a combined form of the first solder bump 5a and second solder bump 5b is indicated as the solder bump 5. By this solder bump 5, the electrode included in the semiconductor chip 2 and the plural lines of the plastic substrate 1 are electrically connected (see FIG. 5(b)). Moreover, after cleaning the flux material, the ring 4 is adhered to the plastic substrate 1 through the first adhesive layer 7a (see FIG. 5(c)). Next, a synthetic resin for sealing is injected in the gap between the plastic substrate 1 and semiconductor chip 2, and solidified to form a sealing member 8, and through this sealing member 8, the semiconductor chip 2 is fixed tightly to the plastic substrate 1. Then, the adhesives are applied on the surface of the semiconductor chip 2, and a second adhesive layer 7b is formed (see FIG. 6(a)), and the adhesives are applied on the surface of the ring 4 to form a first adhesive layer 7a, and the heat spreader 3 provided on the semiconductor chip 2 and ring 4, and the heat spreader 3 is adhered to the semiconductor chip 2 and ring 4 (see FIG. 6(b)). Finally, solder balls 6 formed on the external electrode of the semiconductor device connected to the other end of the plural lines of the plastic substrate 1, and a semiconductor device is obtained (see FIG. 6(c)).
In the conventional semiconductor device, a plastic substrate is used when forming the BGA substrate. The plastic substrate is relatively easy to permeate moisture. Therefore, in the process of use of semiconductor device, the sealing member may deteriorate due to moisture taken into the semiconductor device through the plastic substrate. As a result, the adhesion between the sealing member and plastic substrate may be weaker.
In consideration of such problem, for example, Japanese Unexamined Patent Publication No. 288686/1996 discloses a semiconductor device capable of preventing moisture absorption into the plastic substrate by forming a thin metal film on the surface of the semiconductor device by electroless plating. Such thin metal plate, however, may have effects on the electric characteristic of the semiconductor device, and it cannot be formed in the region where solder bumps are formed, and therefore it is not an effective measure of solving the problem in spite of the high manufacturing cost.
It is hence an object of the invention to solve the above problems and present a semiconductor device strong in adhesion between the sealing member and plastic substrate.